The invention relates to a cable for a structure, especially a suspension bridge, and a process of making it.
A cable of tension elements inside a sheath with a space therebetween filled with a material, for example, injected mortar, has been found practical for suspending a bridge of prestressed concrete construction. For strength, resistance to corrosion, and ease of anchoring, steel bars and, preferably, threaded steel bars should be used for the tension elements. Under certain circumstances, however, e.g., when there is little or no variation in the sag of the cable, stranded steel cables can be used. Either plastic or steel tubing can be used for the sheath.
Such cables are usually prepared in full at the worksite. The tension elements and sheath, but usually not the material filling the rest of the space in the sheath, can also be preassembled, however, and unwound from a drum at the worksite, for example. In either case, the full length of sheathed tension elements for each cable is laid out, hoisted to its final position between two, end-anchoring points, tensioned, and finally, after the sheath has been closed, cement mortar forced therein.
This cable preparation and installation work is time consuming and calls for a high technical knowledge. For example, sheathing tubes of steel have had to be cleanly welded so as to avoid any point at which corrosion might later attack the cable due to poor welds. Sheathing tubes, whether steel or plastic, have also had to be treated such that they are not damaged, for example when the cable is being unwound from a drum or hoisted into place. Not only can such damage serve as a starting point for later corrosion, as previously mentioned, but also it can affect the tensile strength of the cable. Avoiding damage in unwinding and hoisting the sheathed tension elements is difficult, however, because these are so heavy that heavy equipment must be used in order to handle them. All in all, the above-mentioned difficulties increase the final cost of installing such cable.
The idea of providing a cable having a wrapping about a plurality of thin-wire tension elements after an anticorrosive substance has been applied to the tension elements at the place where the cable is prepared, such as a worksite, for example, is disclosed in German Federal patent publication DE-OS No. 15 51 192. However, to use such a cable in a suspension bridge, it must still be first prepared full-length and then installed as described above and, therefore, with the difficulties mentioned.